If expat is installed, but in a non-standard directory, then use the
following options to Makefile.PL:
 
    EXPATLIBPATH=...  To set the directory in which to find libexpat
 
    EXPATINCPATH=...  To set the directory in which to find expat.h
 
For example:
 
    perl Makefile.PL EXPATLIBPATH=/home/me/lib EXPATINCPATH=/home/me/include